1. Field of the Invention
The invention relates to the drilling of wells offshore; and, more particularly, to a method and apparatus for producing hydrocarbons from subterranean formations under the ocean floor.
2. Description of the Prior Art
In an attempt to locate new oil fields, an increasing amount of well drilling has been conducted at offshore locations, such as off the coasts of California, Louisiana, and Texas, and more recently, off the coast of Alaska and in the North Sea. Generally, well drilling structures used at these locations are installed above the surface of the offshore body of water, these structures being supported by columnar frames extending downward to the bottom of the body of water. Straight well conductors generally comprising hollow sections of pipe are extended from these well drilling structures some distance below the ocean floor. These conductors provide guidance and support for tubular well drilling equipment carried within these conductors and used for drilling into hydrocarbon bearing reserves.
As the water depths of the drilling operations increase the cost of these bottom supported well drilling structures becomes prohibitive. For this reason, Tension Leg Platforms, comprising moored floating vessels, or dynamically positioned floating vessels are used in these greater water depths. Wells drilled from these devices are guided through a well conductor template placed below these devices on the ocean floor. This template, generally a massive structure, allows the placement of straight well conductors down through well conductor guides carried by the template, such as disclosed in FIG. 1 of U.S. Pat. No. 4,198,179, entitled "Production Riser," filed Aug. 11, 1978 and issued Apr. 15, 1980 to Floyd T. Pease, et al.
As can be imagined, these structures are expensive, and the number of hydrocarbon bearing reservoirs that may be laterally reached beneath each structure needs to be maximized. But the lateral reach of the well conductors is limited by the vertically oriented well conductor guides carried by the well template. Since the well conductors pass vertically through the well template, wells drilled through these well conductors cannot developed an angle of inclination sufficient to reach distant hydrocarbon bearing formations.
To increase the lateral reach of the wells drilled from the bottom supported marine structures mentioned earlier, curved well conductors were sometimes used as is disclosed in U.S. Pat. No. Re. 28,860, entitled "Curved Offshore Well Conductors", reissued June 15, 1975 to Peter W. Marshall et al. By curving these conductors, the well drilling equipment could develop an angle of inclination from the vertical before leaving the curved conductor. Since the drilling equipment would also develop an early angle of inclination, more distant reservoirs located at a greater lateral distance beneath the marine drilling structure could be reached.
It would be desirable therefore, to also incorporate these curved well conductors into the well templates in order to maximize the lateral reach of the well drilling equipment.
But the probability of successfully aligning and installing curved well conductors into a well template located a substantial distance below a floating drilling vessel must be viewed with apprehension. Poor visibility and strong currents, as well as roll, pitch, heave, and sway of the surface vessel must necessarily complicate the operation.
A method and apparatus needs to be developed which allows the installation of curved well conductors into a subsea well template, in order to maximize the possible economic recovery of hydrocarbon reserves located beneath these well templates.